Users of wet shaving razors are susceptible to excessive nicking and cutting. There are many possible explanations for this, but one of them is how the razor blade moves or glides over the skin. Moreover, as the number of razor blades per cartridge increases, the total blade drag on skin against the skin can also increase.
Most razor blades on the market are produced by applying one or more coatings such as thin film hard coatings to sharpened stainless steel substrates. These coatings may typically deposited on blade edges by Physical Vapor Deposition (PVD) techniques which include vacuum conditions where raw materials, referred to as target materials, i.e., the material that is going to be deposited, are generally in solid form. Common PVD techniques incorporate processes such as sputter coating or Pulsed Laser Deposition (PLD).
Blade coatings were developed to minimize the irritation produced by excessive pulling of hairs which generally may continue for a considerable period of time after the pulling has ceased.
Thin hard coatings have certain roles and advantages. One advantage is that the hard coatings generally strengthen blade edges, particularly those with slim profiles, by providing reinforcement to the edges, thus protecting the edges from excessive damage during shaving.
In addition, since conventional razor blades used for wet shaving generally have increasing cutting forces with use, due to the outer coating wear and adhesion loss, most commercial razor blades also include one or more subsequent depositions of outer coatings (e.g., TEFLON® or telomer coatings, or other polymeric material coatings.
A thin polymer coating on the blade edge is generally lubricious with an inherent hydrophobic nature which causes a film of water droplets of a microscopic scale to remain on the cutting blade edge. This in turn enhances the effect of the polymer coating, and can reduce the frictional resistance between the blade edge and the skin and thereby reduce the cutting force of the hair, greatly improving shaving comfort. Such coatings are described, for example, in U.S. Pat. Nos. 5,645,894 and 5,263,256, the entire disclosures of which are incorporated by reference herein.
In general, this polymer coating is applied only to the tip of the razor blade (e.g., the last 25-50 μm) as it is generally sprayed onto blades edges which are generally arranged in a stack of blades. In some instances, over-spraying and inconsistency of the sprayed polymer are known consequences.
Accordingly, a significant portion of the razor blade is not covered with the lubricious coating but instead maintains some contact with the skin. This may be a disadvantage generally as frictional resistance may remain in uncoated areas, resulting in more tug and pull of a user's skin.
It is an object of the invention to provide a razor blade with improved skin protection, (e.g., comfort and safety) by improving the way the blade or blades in a cartridge glides or moves over the skin, thus minimizing the number of nicks and cuts experienced by a user, while also maintaining or improving rinsability of the razor cartridge.
It is an object of the invention to provide an improved lubricious coating on a razor blade and an improved method of producing such a razor blade.